Voltage and current references are widely used in integrated circuits. Such references exhibit little dependence on supply and temperature. The objective of reference is to establish dc voltage or current that is independent of the power supply and process and has a well-defined behavior with temperature. Since 1980s bandgap reference was invented, it has been widely used in various analog circuits. However, even if the process works in small variations, traditional bandgap reference also has its limitations, which are mainly due to non-linear relationship between output voltage and temperature. This non-linear relationship of the traditional bandgap reference can be explained in FIG. 1. Although the devices are perfectly matched, the output voltage deviation will still be 35 ppm from −20° C. to 100° C. for first order compensation. Such deviation is undesirable in many applications. The bandgap voltage reference shown in FIG. 1 includes the first bipolar transistor Q1, the second bipolar transistor Q2, the output module consisted of field-effect transistor MN1 (N-type), the adjustment module consisted of operational amplifier OP and the resistor network consisted of resistors R1˜R4. One node of the fourth resistor R4 is connected to MN1 as the output port of the output module. The other node of R4 is connected the third resistor R3 and the second resistor R2. The other node of the third resistor R3 is connected with the positive input of operational amplifier OP. The node is connected to ground by the first bipolar transistor Q1. The other node of the second resistor R2 is connected to the negative input of operational amplifier OP, and is then connected to ground by the first resistor R1 and the second bipolar transistor Q2. Q1 and Q2 shown in FIG. 1 are fabricated by typical CMOS process, the emitter area ratio of them are AE1/AE2. The operational amplifier OP clamps the voltage on R2 and R3 to be equal. The voltage on R1 can be given as:VPTAT=VVBE=VBE2−VBE1 
This voltage is directly proportional to absolute temperature:
      V    PTAT    =            kT      q        ⁢          ln      ⁡              (                              A                          E              ⁢                                                          ⁢              1                                            A                          E              ⁢                                                          ⁢              2                                      )            (T is absolute temperature, K is the Boltzmann factor, q is electric charge of carrier)
The output voltage VREF can be given as:VREF=VBE+KVVBE  (1)
Where K is a factor which is used to compensation the first order temperature coefficient of VBE. K is determined by the resistor network.
The bandgap voltage references mentioned above are almost the prototype of all the bandgap references. Although it has been designed perfectly match, the output voltage will also have a 35 ppm deviations in −20° C.˜100° C. which are caused by the curvature of the temperature characteristic curve for VREF. As shown in FIG. 3, when the resistance varies, the output voltage changes with temperature. Such deviation is still undesirable in many applications. Lots of curvature correction techniques have been invented, but most of the techniques are to compensate high order temperature coefficient. The compensation term is difficult to generate in the standard CMOS technology and the high order compensation is sensitive to process.
The temperature deviations of traditional bandgap reference are large and the high order compensation is difficult to implement. This invention's objective is to provide bandgap reference which uses the lower order (first order) compensated bandgap voltage reference to generate reference voltage with much lower temperature coefficient.